1. Field of the Invention
The present invention relates to a steam turbine plant.
2. Description of the Related Art
Conventional steam turbine plants include one disclosed in JP, A 60-159310, for example. JP, A 60-159310 discloses a steam turbine having a dual casing structure composed of an inner and an outer casing wherein the space between the inner and outer casings is divided by a partition wall into a first steam passage allowing part of main steam to pass along the outer surface of the inner casing and a second steam passage allowing cooling steam to pass along the inner surface of the outer casing, and wherein an opening/closing device is provided to each of the first and second steam passages, whereby thermal stress in the inner and outer casings is reduced even if this steam turbine is frequently started and stopped. JP, A 60-159310 further discloses a structure wherein main steam piping line for supplying a steam from a boiler is connected to an upper portion of the outer casing, and wherein an exhaust hole is provided for discharging exhaust steam that has worked at various stages of the turbine and sending it to a next turbine.